Liquid crystal display device

ABSTRACT

A liquid crystal display device including a thin light guide plate and capable of preventing light leakage from light sources is provided. The light guide plate is formed of a sheet. On a back face of the light guide plate, a first projection and a second projection that protrude outwardly and a reflection face provided between the first projection and the second projection are provided. The light sources are disposed on a side face of the light guide plate. A light entering portion is disposed on the side face where the light source is provided. A thin film portion is included between the light sources adjacent to each other in the light entering portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2009-009253 filed on Jan. 19, 2009, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device.

2. Background Art

In recent years, liquid crystal display devices are widely used asinformation display devices of mobile equipment. For miniaturizing themobile equipment, liquid crystal display devices are required to reducethe entire thickness.

On the other hand, since liquid crystal display devices are notself-luminous, a planar lighting unit called a backlight is required inmany cases. In the liquid crystal display device used for mobileequipment, a method has been known in which a light source is providedon the side face of a light guide plate as a planar lighting unit forreducing the thickness of a backlight. In such a planar lighting unit,an appropriate structure is provided for the light guide plate foruniformly scattering light introduced from the side face to the frontface. In the planar lighting unit, it must be noted that unnecessarylight should not reflect in the screen.

For example, JP-A-7-43710 discloses a liquid crystal display device inwhich a plurality of grooves having protrusions that protrude outwardlyon both ends of an opening are provided on the surface of a light guideplate. In the liquid crystal display device, light incident on theprotrusion exits outwardly, is irregularly reflected by a reflector, andthen enters again the light guide plate.

Further, JP-A-2005-251687 discloses a liquid crystal display device inwhich a light source is provided on the side face of a light guide plateand a light shielding material is provided on a flexible printed circuitto prevent the color of the flexible printed circuit from beingreflected in a screen.

SUMMARY OF THE INVENTION

Light guide plates are generally manufactured by injection molding atransparent thermoplastic resin such as polycarbonate orpolymethylmethacrylate. According to the method, however, it isdifficult to obtain a light guide plate thinner than a certainthickness, for example, having a thickness of 1 mm or less because ofthe insufficient filling of a resin into a metal mold or the difficultyof removing a product from a mold.

Moreover, in the planar lighting unit in which a light source isprovided on the side face of a light guide plate, light from the lightsource leaks into a screen, which causes brightness non-uniformity ofthe screen near the light source.

The invention has been made from the above-described standpoint, and itis an object of the invention to provide a liquid crystal display deviceincluding a thin light guide plate having a thickness of, for example, 1mm or less. It is another object of the invention to provide a liquidcrystal display device that can prevent light leakage from a lightsource.

Typical outlines of the invention disclosed herein will be brieflydescribed below.

A liquid crystal display device includes: a liquid crystal panel havinga liquid crystal layer interposed between a first substrate and a secondsubstrate; a light guide plate disposed on a back face side of theliquid crystal panel, the light guide plate including a reflection faceon a back face thereof, a first projection and a second projectionformed so as to interpose the reflection face therebetween, and a lightentering portion disposed on a side face thereof; and light sourcesdisposed so as to face the light entering portion, wherein a lightshielding member is formed between the liquid crystal panel and thelight guide plate.

The light shielding member has a frame shape with four sides, and a sideoverlapping the light entering portion has a greater width than that ofthe others. The light shielding member has a frame shape with foursides, and a notch portion is formed on both ends of a side overlappingthe light entering portion.

The light shielding member has a frame shape with four sides, and a sideoverlapping the light entering portion is cut off from the others. Thelight shielding member has a frame shape with four sides, and the lightshielding member is a black two-sided adhesive tape.

A liquid crystal display device includes: a liquid crystal panel havinga liquid crystal layer interposed between a first substrate and a secondsubstrate; a light guide plate made of a thermoplastic material anddisposed on a back face side of the liquid crystal panel, the lightguide plate including a reflection face on aback face thereof, a firstprojection and a second projection formed so as to interpose thereflection face therebetween, and a light entering portion disposed onaside face thereof; and a plurality of light sources disposed so as toface the light entering portion, wherein the height of the lightentering portion is greater at a portion facing the light source andsmaller at a portion interposed between the light sources.

A padding is disposed at the portion of the light entering portioninterposed between the light sources and having a smaller height. Thepadding is a two-sided adhesive tape.

According to the invention disclosed herein, it is possible to provide aliquid crystal display device including a thin light guide plate havinga thickness of, for example, 1 mm or less. It is also possible toprovide a liquid crystal display device that can prevent light leakagefrom a light source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a liquid crystal display device accordingto an embodiment of the invention.

FIGS. 2A and 2B are schematic views of a light emitting diode as a lightsource.

FIGS. 3A and 3B are schematic views of a light guide plate.

FIG. 4 is an explanatory view of light reflected by a groove.

FIG. 5 shows the state where a mold is pressed onto a sheet.

FIG. 6 shows the sheet removed from the mold.

FIG. 7 shows a modification of the light guide plate with regard to thegroove.

FIG. 8 shows the state of forming the groove of the modification.

FIG. 9 is a perspective view of the vicinity of an incident face of thelight guide plate.

FIGS. 10A and 10B each illustrate the shape of a lens.

FIG. 11 is a plan view showing the light guide plate punched from thesheet.

FIG. 12 shows a modification of a light entering portion.

FIG. 13 shows a modification of the light entering portion.

FIG. 14 shows an attaching structure for attaching the light emittingdiode to the light guide plate.

FIG. 15 is a cross-sectional view of the liquid crystal display device.

FIG. 16 is a reference cross-sectional view of a liquid crystal displaydevice in which an extended portion is not provided.

FIGS. 17A to 17D each show the shape of alight shielding member.

FIG. 18 shows the shape of a light shielding member.

FIG. 19 shows the shape of a light shielding member.

FIG. 20 shows the shape of a light shielding member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a preferred embodiment of the invention will be describedwith reference to the drawings.

FIG. 1 is a plan view showing a liquid crystal display device 100according to the embodiment. The liquid crystal display device 100includes a liquid crystal panel 1, a backlight 110, and a controlcircuit 80. Signals and power supply voltage necessary for the displayof the liquid crystal display device 100 are supplied from the controlcircuit 80. The control circuit 80 is mounted on a flexible substrate70. Signals are transmitted to the liquid crystal panel 1 via wiringwires 71 and terminals 75. The liquid crystal panel 1 functions as alight switching member that controls light transmittance.

The backlight 110 includes a light guide plate 120, light emittingdiodes 150 as light sources, and a housing case 180. The backlight 110is provided for irradiating the liquid crystal panel 1 with light. Inthe liquid crystal panel 1, the transmission amount of the lightirradiated from the backlight 110 is controlled to perform display. Thebacklight 110 is overlapped with the liquid crystal panel 1 with respectto an observer. In FIG. 1, however, the backlight 110 and the liquidcrystal panel 1 are arranged vertically for facilitating theunderstanding. In the specification below, a direction in which theliquid crystal display device 100 faces an observer is referred to as afront face side, and the opposite direction is referred to as a backface side. A face of the liquid crystal display device 100 on the frontface side is referred to as a front face, and a face on the back faceside is referred to as a back face. The backlight 110 is generallydisposed on the back face side of the liquid crystal panel 1, but may bedisposed on the front face side. In such a case, the liquid crystalpanel 1 controls the reflection amount of the light irradiated from thebacklight 110.

The light guide plate 120 has substantially a rectangular shape. Thelight emitting diodes 150 are provided so as to face an incident face125 as one side face of the light guide plate. Reference numeral 160denotes a flexible substrate that electrically connects the plurality oflight emitting diodes 150 with one another. The flexible substrate 160and the control circuit 80 are electrically connected to each other viaa wiring wire 161.

Light incident from the incident face 125 to the light guide plate 120exits from an exit face 121 as a front face of the light guide plate.Inclined faces 127 are formed between the incident face 125 and the exitface 121 and guide light from the incident face 125 to the exit face121. The incident face 125 and the inclined faces 127 form a lightentering portion 124 through which the light from the light emittingdiodes 150 is effectively transmitted to the exit face 121. The incidentface 125 and the light entering portion 124 will be described in detaillater.

Next, the liquid crystal panel 1 will be described. The liquid crystalpanel 1 has two substrates of a TFT substrate 2 and a color filtersubstrate 3. A liquid crystal composition is interposed between the twosubstrates stacked to each other. A plurality of pixel portions 8 areprovided on the TFT substrate 2. A pixel electrode 12 is provided ineach of the pixel portions 8. The plurality of pixel portions 8 arearranged in a grid in a display region 9. Each of the pixel portions 8functions as a light switching element that controls the transmissionamount of the light from the backlight 110, thereby functioning as apixel of the liquid crystal display device 100 to form an image in thedisplay region 9. For preventing the drawing from being complicated,FIG. 1 shows only one pixel portion 8.

In FIG. 1, gate signal lines (also referred to as scanning lines) 21extending in the x direction in the drawing and arranged in parallel inthe y direction and drain signal lines (also referred to as video signallines) 22 extending in the y direction and arranged in parallel in the xdirection are provided. The gate signal lines 21 and the drain signallines 22 cross each other. The pixel portion 8 is formed in a regionsurrounded by the gate signal lines 21 and the drain signal lines 22.

A switching element 10 such as a TFT (Thin Film Transistor) is providedin the pixel portion 8. A control signal is supplied from the gatesignal line 21 to control the on and off of the switching element 10.When the switching element 10 is brought into an on state, a videosignal transmitted via the drain signal line 22 is supplied to the pixelelectrode 12.

The drain signal lines 22 are connected to a drive circuit 5. Videosignals are output from the drive circuit 5. The gate signal lines 21are connected to a drive circuit 6. Control signals are output from thedrive circuit 6. The gate signal lines 21, the drain signal lines 22,the drive circuit 5, and the drive circuit 6 are formed above the sameTFT substrate 2. The drive circuit 5, the drive circuit 6, and thecontrol circuit 80 can be formed above one semiconductor chip.

The driving method of liquid crystal in the liquid crystal panel 1 isnot specifically limited. Any of a TN (Twisted Nematic) system, a VA(Vertical Alignment) system, and an IPS (In Plane Switching) system maybe used.

Next, FIGS. 2A and 2B are schematic views of the light emitting diode150 as a light source. FIG. 2A is a schematic cross-sectional view. FIG.2B is an elevation view of a light exiting side.

The light emitting diode 150 has a light emitting diode chip 151 as alight emitting portion mounted on a chip substrate 154. The lightemitting diode chip 151 has a pn junction and emits light at a specificwavelength when voltage is applied to the pn junction. A p-electrode(anode) 158 and an n-electrode (cathode) 159 are respectively providedin a p type semiconductor layer and an n type semiconductor layer thatform the pn junction.

Wires 152 are each connected to the p-electrode 158 and the n-electrode159. The wires 152 electrically connects the chip terminals 153 providedfor connecting the light emitting diode 150 to the outside with thep-electrode 158 and the n-electrode 159.

A fluorescence emitting portion 156 is provided on the exit face side ofthe light emitting diode chip 151 in some cases. The fluorescenceemitting portion 156 has a function of converting the wavelength oflight emitted from the light emitting diode chip 151. Reference numeral155 denotes a reflection portion that reflects light forward. An exitface 157 from which light exits is formed on the front face side of theLED 150.

Next, FIGS. 3A and 3B are schematic views of the light guide plate 120.FIG. 3A is a schematic plan view. FIG. 3B is a schematic side view. Thelight guide plate 120 has substantially a rectangular shape as shown inFIG. 3A and has the exit face 121 as a front face and a back face 122 asshown in FIG. 3B. The light guide plate 120 is formed of alight-transmissive thermoplastic material such as polycarbonate orpolymethylmethacrylate and has a sheet shape. The thickness thereof ispreferably from 1.0 mm to 0.1 mm. Here, the thickness of the light guideplate 120 means the interval between the exit face 121 and the back face122.

Although a cross section of the light guide plate 120 is substantially arectangular shape in FIG. 33, the inclined face 127 is formed so as tobe smoothly continuous from the incident face 125 to the exit face 121.As shown in FIG. 3A, the inclined face 127 has a shape of an unfoldedfan extending from the light emitting diode 150 in a direction (in the xdirection in the drawing) remote from the optical axis direction of thelight emitting diode 150 when the light guide plate 120 is viewed in aplane. The inclined face 127 is effective when the thickness of thelight emitting diode 150 is greater with respect to the thickness of thelight guide plate 120 at the exit face 121.

FIGS. 3A and 33 show the positional relationship among the light guideplate 120, the light emitting diodes 150, and the flexible substrate160. The incident face 125 is provided on at least one side of the lightguide plate 120. The plurality of light emitting diodes 150 are providedin the vicinity of the incident face 125. The light emitting diodes 150are arranged along the incident face 125 below the flexible substrate160.

An intermediate member (not shown) such as a two-sided adhesive tape isprovided on the light-guide-plate 120 side of the flexible substrate160. The flexible substrate 160 is bonded and fixed to the light guideplate 120, so that the position of light emitting diode 150 is alignedto the incident face 125.

Next, a light 140 emitted from the light emitting diode 150 will bedescribed by using FIG. 3B. The light 140 exiting from the lightemitting diode 150 is incident on the light guide plate 120 through theincident face 125. The refractive index of the light guide plate 120 isgreater than that of air. Therefore, the light 140 reaching the incidentface 125 at an angle greater than a specific angle with respect to thenormal direction of the incident face 125 is reflected. The light 140reaching the incident face 125 at an angle smaller than the specificangle enters into the light guide plate 120.

The exit face 121 and the back face 122 of the light guide plate 120 aresubstantially perpendicular to the incident face 125. The light enteredinto the light guide plate 120 propagates through the light guide plate120 while repeating total reflection at the exit face 121 and the backface 122 of the light guide plate 120. The back face 122 is providedwith V-shaped grooves 126 as a reflection portion. A part of the light140 propagating through the light guide plate 120 is reflected towardthe exit-face 121 side by the groove 126 provided on the back face 122and exits from the exit face 121. The grooves 126 are provided in adirection substantially perpendicular to the optical axis direction ofthe light emitting diode 150.

Next, the light 140 that is reflected by the groove 126 will bedescribed by using FIG. 4. In FIG. 4, prism sheets 112 and 113, adiffuser 114, and a reflective sheet 115 are shown in addition to thelight guide plate 120. It is assumed that the light emitting diode 150is arranged on the left in the drawing. The grooves 126 constitute thesurface structure formed on the back face 122 of the light guide plate120. The groove 126 includes a first projecting face 128 that protrudesoutwardly from the back face 122, a first light reflecting face 129 thatis continuous from the first projecting face and enters the inside ofthe back face 122, a second light reflecting face 130 that is continuousfrom the first light reflecting face 129 and protrudes to the outside ofthe back face 122, and a second projecting face 131 that is continuousfrom the second light reflecting face to the back face 122 in this ordertoward the optical axis direction of the light emitting diode 150. Thefirst light reflecting face 129 and the second light reflecting face 130have an angle of from 1 degree to 35 degree with respect to the backface 122. In the embodiment, the light 140 exiting from the lightemitting diode 150 and propagating through the light guide plate 120 ismainly reflected by the first light reflecting face 129 and changes itstraveling direction so as to have an angle at which the light 140 canexit from the exit face 121. That is, as described above, the light 140repeats total reflection in the light guide plate 120 and propagatestoward the optical axis direction of the light emitting diode 150.However, mainly due to the first light reflecting face 129, the light140 has an angle at which the light can exit and exits from the exitface 121 of the light guide plate 120.

It is needless to say that the second light reflecting face 130functions in the same manner as the first light reflecting face 129 whenthe light emitting diode 150 as a light source is further arranged onthe right in the drawing.

In the embodiment, grooves 132 having the same surface structure as thegrooves 126 of the back face 122 are provided on the exit face 121 ofthe light guide plate 120 so as to be substantially perpendicular to thegrooves 126. The groove 132 functions to deflect the light 140 reflectedby the first light reflecting face 129 toward the front face side of thelight guide plate 120. The light 140 exiting from the light guide plate120 is diffused by the diffuser 114 and then changes its directiontoward the front face side of the light guide plate 120 by the prismsheets 113 and 112. The prism sheets 113 and 112 are transparent sheetseach having a triangular prism-shaped surface structure on the surface.They are arranged such that the directions of the triangularprism-shaped surface structures are perpendicular to each other. Thereflective sheet 115 reflects the light 140 exiting toward the back faceof the light guide plate 120 and introduces the same again into thelight guide plate 120. Since the prism sheet 113 and the grooves 132 aresimilar to each other in operation and effect, either one of them may beomitted if unnecessary.

In the embodiment, the light guide plate 120 is thin and easilydeformed. However, a protrusion 133 formed of the first projecting face128 and the first light reflecting face 129, or the second projectingface 131 and the first light reflecting face 130 prevents the closecontact of the light guide plate 120 with the reflective sheet 115. Thisprovides an effect of suppressing the non-uniformity of brightnessdistribution or light leakage caused by the close contact of the lightguide plate 120 with the reflective sheet 115.

Next, a method for forming the grooves 126 will be described. In theembodiment as described above, since the light guide plate 120 is asthin as 1.0 mm to 0.1 mm, it is difficult to form the grooves 126 byinjection molding. Therefore, the grooves 126 are formed by a methodincluding the following steps.

First Step

A sheet 170 made of a thermoplastic material is heated to be softened(heating step). When the sheet 170 is a thermoplastic resin such aspolycarbonate or polymethylmethacrylate, the heating temperature may beset to the softening point or more of the thermoplastic resin. When thesheet 170 is glass, the temperature may be set to the glass-transitionpoint or more.

Second Step

A mold 171 is pressed onto the sheet 170 (pressing step). The mold 171is preferably a metal mold made of metal and has a number of triangularprism-shaped ridges 172 formed on the surface. The mold 171 is pressedsuch that the ridge 172 bites into the surface of the sheet 170 in apredetermined amount. FIG. 5 shows the state where the mold 171 ispressed onto the sheet 170. As shown in FIG. 5, the thermoplasticmaterial constituting the sheet 170 is pressed by the ridge 172 andflows as indicated by arrows 173. As a result, on one hand, the firstlight reflecting face 129 and the second light reflecting face 130 areformed at a portion where the sheet 170 is brought into contact with theridge 172 of the mold 171. On the other hand, the first projecting face128 and the second projecting face 131 are formed as free surfaces atportions to which the thermoplastic material constituting the sheet 170flows to project without being in contact with the mold 171.

Third Step

The sheet 170 is removed from the mold 171 (removing step). In thiscase, the sheet 170 may be cooled if necessary. As is apparent from FIG.5, in the embodiment, the sheet 170 and the mold 171 are in contact witheach other only at the ridge 172 of the mold 171 but not on the entiresurfaces thereof. Therefore, the sheet 170 is easily removed from themold 171. According to the method, therefore, the thin light guide plate120 can be obtained from the thin sheet 170 having a thickness of aboutfrom 1.0 mm to 0.1 mm.

FIG. 6 shows the sheet 170 removed from the mold 171. In this case,before and after the formation of the grooves 126 by the above-describedmethod, the sheet 170 does not change in volume. Accordingly, whenattention is directed to the groove 126, the volume of the thermoplasticmaterial positioned on the surface of the sheet 170 and on the outsideof a face serving as the back face 122 of the light guide plate 120,that is, the portions indicated by A in the drawing and the volume of aspace portion positioned inside the back face 122, that is, the portionindicated by B in the drawing are equal to each other.

FIG. 7 shows a modification of the light guide plate 120 with regard tothe groove 126. As shown in FIG. 7, an angle that the first lightreflecting face 129 of the groove 126 makes with the back face 122 maydiffer from an angle that the second light reflecting face 130 makeswith the back face 122. In this case, when the first light reflectingface 129 intersects the back face 122 at a shallow angle, the light 140incident from the left in the drawing exits mainly in a directioninclined to the right in the drawing with respect to the verticaldirection of the exit face 121. An asymmetrical prism sheet 116 isprovided above the light guide plate 120 via the diffuser 114 to deflectthe direction of the light 140 toward the front face side of the lightguide plate 120. With this configuration, since a rate of the light 140incident on the first light reflecting face 129 at a shallow angle isincreased, a rate of the light 140 reflected toward the front face sideis increased. Therefore, the use efficiency of the light 140 can beenhanced. Also in the modification, the prism sheet 113 may be providedlike the foregoing example.

FIG. 8 shows the state of forming the groove 126 of the modification.FIG. 8 differs from FIG. 5 in that the ridge 172 of the mold 171 isbilaterally asymmetric. Also in this case, the thermoplastic materialconstituting the sheet 170 flows as indicated by the arrows 173, so thatthe first projecting face 128 and the second projecting face 131 areformed as free surfaces. The first light reflecting face 129 and thesecond light reflecting face 130 are formed while being in contact withthe ridge 172 of the mold 171.

Consequently, a structure of the vicinity of the incident face 125 ofthe light guide plate 120 will be described. FIG. 9 is a perspectiveview of the vicinity of the incident face 125 of the light guide plate120. A plurality of light introducing portions 134 and a plurality oflight non-introducing portions 135 are provided on the incident face125. The light introducing portion 134 has a thickness greater than thatof the light guide plate 120. The light non-introducing portion isprovided at a portion interposed between the light introducing portions134 and a portion interposed between the light introducing portion 134and an end of the light guide plate 120. The light non-introducingportion has a thickness smaller than that of the light guide plate 120.Therefore, the incident face 125 has a shape with concavities andconvexities on the front face side of the light guide plate 120 asviewed from the normal direction of the incident face. In this case, thelight introducing portions 134 correspond to the convexities, while thelight non-introducing portions 135 correspond to the concavities. An endside of the light introducing portion 134 on the front face side isconnected to the exit face 121 so as to be smoothly continuous with theexit face with the inclined face 127. On the other hand, an end side ofthe light non-introducing portion 135 on the front face side isconnected to the exit face 121 in parallel therewith a concave face 136.A level difference is formed at the connecting portion of the concaveface and the exit face. Lenses 123 are provided in the light introducingportion 134 of the incident face 125. The lens 123 scatters lightincident from the light introducing portion 134. The light incident fromthe light introducing portion 134 is introduced to the exit face 121through the inclined face 127. The incident face 125 formed of the lightintroducing portions 134 and the light non-introducing portions 135, theinclined faces 127, and the concave faces 136 form the light enteringportion 124.

As described above, the thickness of the light introducing portion 134is made greater than that of the light guide plate 120, so that thelight guide plate 120 thinner than the light emitting diode 150 can beused. Preferably, the thickness of the light introducing portion 134 ismade substantially equal to that of the light emitting diode 150.

Although various kinds of shapes can be adopted for the lens 123, ashape extending in a thickness direction of the light guide plate 120 ispreferred. This is because, as will be described later, the light guideplate 120 is prepared by punching the sheet 170. Therefore, the lens 123has preferably a shape to be easily punched. For example, a shape havinga triangle cross-section as shown in FIG. 10A and a shape obtained byjoining a plurality of cylindrical lenses having a semicircle shape asshown in FIG. 10B can be illustrated. In view of the easiness of theprocess, it is preferable to select a shape of lens with a roundedcorner. However, a general shape of lenticular lens or a saw-tooth shapemay be adopted.

Next, a method for forming the light entering portion 124 and a methodfor manufacturing the light guide plate 120 will be described. The lightentering portion 124 is formed by a method including the followingsteps.

First Step

The sheet 170 made of a thermoplastic material is heated to be softened(heating step). The heating temperature is the same as in the method forforming the groove 126. In this case, the size of the sheet 170 ispreferably set to be larger than that of the light guide plate 120 to beobtained. The thickness of the sheet 170 is equal to that of the lightguide plate 120 to be obtained.

Second Step

A mold is pressed onto the sheet 170 (pressing step). Also the mold inthis case is preferably a metal mold made of metal. The mold has a shapecomplementary to the light entering portion 124 of the sheet 170.Therefore, the thermoplastic material at a portion serving as theconcave face 136 of the sheet 170 is pressed to flow into a portionserving as the inclined face 127 of the sheet 170. As a result, aportion serving as the light introducing portion 134 having a thicknessgreater than that of the sheet 170 is formed. In this case, the grooves126 and the grooves 132 may be formed simultaneously or may be formed ina different step.

Third Step

The sheet 170 is removed from the mold (removing step). In this case,the sheet 170 may be cooled if necessary.

Fourth Step

The outer circumference of the sheet 170 is cut out, so that the lightguide plate 120 having the light entering portion 124 is obtained(cutting-out step). FIG. 11 is a plan view showing the light guide plate120 cut out from the sheet 170. The lens 123 is formed by the step.Since punching process is used as a cut-out method in the embodiment,corners 137 of the light guide plate 120 are slightly rounded forfacilitating the process.

In the manufacture of the light guide plate 120 according to the method,one light guide plate 120 may be obtained from one sheet 170, or anumber of light guide plates 120 may be cut out from one sheet 170, sothat multiple plates are formed at one time. Moreover, the light guideplate 120 may be manufactured from the sheet 170 having a plate shape bya batch process, or the light guide plate 120 may be manufactured bycontinuously unwinding the sheet 170 having a belt shape from a rawsheet roll by a continuous process. In that case, an embossing roll canbe used as a mold.

FIGS. 12 and 13 show modifications of the light entering portion 124.FIG. 12 shows an example in which the concave face 136 is formed as aninclined face that is smoothly connected to the exit face 121. FIG. 13shows an example in which the concave face 136 is flush with the exitface and the thickness of the light non-introducing portion 135 is thesame as that of the light guide plate 120. The example of FIG. 13 can bemanufactured by pressing a portion of the sheet 170 outside the lightguide plate 120 and making a thermoplastic material flow into a portionserving as the inclined face 127.

Consequently, an attachment structure for attaching the light emittingdiodes 150 to the light guide plate 120 will be described. FIG. 14 showsan attachment structure for attaching the light emitting diodes 150 ofthe embodiment to the light guide plate 120. The light emitting diodes150 are attached to the back face side of the flexible substrate 160 andarranged so as to face the light introducing portion 134. The flexiblesubstrate 160 is fixed to the light guide plate 120 via intermediatemembers 162. In FIG. 14, only the outer shape is shown for the flexiblesubstrate 160 by broken lines for facilitating the understanding.

As shown in FIG. 14, the intermediate member 162 has a shapecomplementary to the concave face 136 and is fixed to the concave face136 at the back face. In other words, the intermediate member 162 isfixed to the exit face 121 as a front face of the light guide plate 120while being adjacent to the light non-introducing portion 135. A frontface of the intermediate member 162 is fixed to the flexible substrate160. The thickness of the intermediate member 162 is preferably equal tothe difference between the thickness of the light introducing portion134 and the thickness of the light non-introducing portion 135. Withthis configuration, a fixing structure is not required between theflexible substrate 160 and the inclined face 127 as a front face of thelight introducing portion 134, by which amount the thickness of theattaching structure can be reduced.

Although the intermediate member 162 is a two-sided adhesive tape in theembodiment, this is not restrictive. The intermediate member 162 may beprepared from an appropriate material. The thickness of the intermediatemember 162 is not necessarily constant. When the concave face 136 is aninclined face as described above, the thickness may be changed alongwith the inclined face. Further, although the flexible substrate 160 isillustrated in a rectangular shape that covers the light enteringportion 124 and the light emitting diode 150, this is not restrictive.The flexible substrate 160 may have any shape as along as it can fix thelight emitting diode 150 via the intermediate member 162.

A structure for preventing light leakage from a light source in theembodiment will be described. FIG. 15 is a cross-sectional view of theliquid crystal display device 100. FIG. 15 shows the positionalrelationship among the liquid crystal panel 1, polarizers 4 and 7respectively attached to the front and back faces of the liquid crystalpanel, the light guide plate 120, the prism sheets 112 and 113 and thediffuser 114 as optical sheets attached to the front face of the lightguide plate, the reflective sheet 115, the light emitting diode 150, andthe flexible substrate 160. The liquid crystal panel 1 and the flexiblesubstrate 160 are attached to the housing case 180 via a light shieldingmember 164. A spacer 163 is inserted between the light shielding member164 and the flexible substrate 160 if necessary. A gap 181 with apredetermined width is provided at a position corresponding to thedisplay region 9.

The light shielding member 164 has a function of preventing light fromentering from the peripheral portion to the display region 9.Preferably, a black two-sided adhesive tape is used for the lightshielding member. The light shielding member 164 has a frame shape in aplan view and fixes the liquid crystal panel 1 and the light guide plate120 to the housing case 180 over the entire outer circumference. In theembodiment, the light shielding member 164 has an extended portion 165extended in a tongue shape from a position corresponding to the lightemitting diode 150 toward the optical axis direction of the lightemitting diode 150. The extended portion 165 bends and hangs in adirection remote to the back face side of the liquid crystal panel 1 andis fixed to the prism sheet 112 as shown in FIG. 15. In other words, theextended portion 165 is indirectly fixed to the light guide plate 120via the prism sheets 112 and 113 and the diffuser 114. The extendedportion 165 may be directly fixed to the light guide plate 120. A frontface of the extended portion 165 as a face on the opposite side may beor may not be fixed to the polarizer 7.

When the extended portion 165 as described above is provided, the light140 exiting from the light emitting diode 150 and leaking from theinclined face 127 to the front face side is blocked by the extendedportion 165, thereby not reaching the display region 9 as shown in FIG.15. It is considered that the leaking from the inclined face 127 is dueto the first projecting face 128 and the second projecting face 131 ofthe groove 132 provided adjacent to the inclined face 127 as shown inFIG. 9.

For facilitating the understanding of the effect, a reference examplewill be described in which the extended portion 165 is not provided inthe liquid crystal display device 100 according to the embodiment. FIG.16 is a reference cross-sectional view of the liquid crystal displaydevice 100 in which the extended portion 165 is not provided. In thereference example, members equal to those of the embodiment are denotedby the same numeral references as in the embodiment, and the detaileddescription thereof is omitted.

As is apparent from FIG. 16, when the extended portion 165 is notprovided, the light 140 exiting from the light emitting diode 150 andleaking to the front face side of the inclined face 127 is incident onthe liquid crystal panel 1 or the polarizer 7 and can reach the displayregion 9 while repeating reflection. Therefore, when the extendedportion 165 is not provided, brightness non-uniformity might be causedin the display region 9.

FIGS. 17A to 17D show various kinds of shapes of the light shieldingmember 164. FIG. 17A shows an example in which a cut portion 166 isprovided toward an outer side of the light shielding member 164 on bothends of one side of a rectangular opening of the light shielding member164 having a frame shape to form the extended portion 165. FIG. 17Bshows an example in which a notch portion 167 having a predeterminedwidth is provided toward the outer side of the light shielding member164 on both ends of one side of the rectangular opening of the lightshielding member 164 having a frame shape to form the extended portion165. FIG. 17C shows an example in which the extended portion 165 havinga rectangular shape is disposed as another member inside an outsidemember 168 having a frame shape to form the light shielding member 164.FIG. 17D shows an example in which the extended portion 165 having arectangular shape is disposed as another member inside a U-shapedoutside member 169 to form the light shielding member 164. The lightshielding member 164 may have any shape as long as it can fix the liquidcrystal panel 1 and the light guide plate 120 to the housing case 180over the entire outer circumference and it can block the light 140leaked from the inclined face 127 to the front face side. Other shapesmay be adopted in addition to the shapes illustrated in FIGS. 17A to17D.

FIG. 18 is a plan view showing the light shielding member 164. The lightshielding member 164 forms a square frame. The light shielding member164 is formed of a cut-off side 238 and the remaining three sides 236.

The light shielding member 164 can be formed only of a black lightshielding layer. Since the black light shielding layer is black, it canabsorb light and reduce reflection of light. Moreover, the black lightshielding layer has conductivity because it is formed of a materialcontaining carbon black. The light shielding member 164 is disposedabove the wiring substrate 160 (opposite side from the light emittingdiode 150). By disposing the light shielding member 164 above the wiringsubstrate 160, light exiting from the wiring substrate 160 can beblocked.

Since the wiring substrate 160 has a chromatic color, light transmittingthrough the wiring substrate 160 has a chromatic color. However, sincethe light shielding member 164 absorbs light, chromatic color light canbe reduced. Therefore, it is possible to reduce the color non-uniformityof a backlight to realize uniform surface emission. When the lightshielding member 164 is used for the cut-off side 238, and a two-sidedadhesive tape is used for the other remaining three sides 236, anincrease in cost for the material can be suppressed.

The light shielding member 164 shown in FIG. 19 has a white lightshielding layer 142 attached to a black light shielding layer 138 on theopposite side from an adhesive layer 140. A second adhesive layer 144 isinterposed between the black light shielding layer 138 and the whitelight shielding layer 142 to bond them together. The light shieldingmember 164 has a second black light shielding layer 146 attached to thewhite light shielding layer 142 on the opposite side from the blacklight shielding layer 138. A third adhesive layer 148 is interposedbetween the white light shielding layer 142 and the second black lightshielding layer 146 to bond them together.

According to the light shielding member 164 shown in FIG. 19, lighttransmitting through the black light shielding layer 138 can be blockedby the white light shielding layer 142. This can further prevent straylight from exiting upwardly from the light shielding member 164.Further, the second black light shielding layer 146 covers the whitelight shielding layer 142 to thereby prevent the white light shieldinglayer from being stained. Since the second black light shielding layeritself is black, stain is not noticeable.

In the light shielding member 164 shown in FIG. 20, a second black lightshielding layer 246 includes a black resin layer 250 containing carbonblack and a black print layer 252 formed of an ink containing carbonblack.

1. A liquid crystal display device comprising: a liquid crystal panelhaving a liquid crystal layer interposed between a first substrate and asecond substrate; a light guide plate disposed on a back face side ofthe liquid crystal panel, the light guide plate including a firstprojection and a second projection formed on a back face thereof, areflection face interposed between the first projection and the secondprojection, and a light entering portion formed on a side face thereof;and a plurality of light sources formed so as to face the light enteringportion, wherein the height of the side face is greater at a portionfacing the light source and smaller at a portion interposed between thelight sources.
 2. A liquid crystal display device according to claim 1,wherein a padding is disposed at the portion interposed between thelight sources.
 3. A liquid crystal display device according to claim 1,wherein a padding is disposed at the portion interposed between thelight sources, and the thickness of the padding is equal to thedifference between the heights of the side face.
 4. A liquid crystaldisplay device according to claim 1, wherein a padding is disposed atthe portion interposed between the light sources, and the padding is atwo-sided adhesive tape.
 5. A liquid crystal display device comprising:a liquid crystal panel having a liquid crystal layer interposed betweena first substrate and a second substrate; a light guide plate made of athermoplastic material and disposed on a back face side of the liquidcrystal panel, the light guide plate including a first projection and asecond projection formed on a back face thereof, a reflection faceinterposed between the first projection and the second projection, and alight entering portion formed on a side face thereof; and a plurality oflight sources formed so as to face the light entering portion, whereinthe height of the side face is greater at a portion facing the lightsource and smaller at a portion interposed between the light sources. 6.A liquid crystal display device according to claim 5, wherein a paddingis disposed at the portion interposed between the light sources.
 7. Aliquid crystal display device according to claim 5, wherein a padding isdisposed at the portion interposed between the light sources, and thethickness of the padding is equal to the difference between the heightsof the side face.
 8. A liquid crystal display device according to claim5, wherein a padding is disposed at the portion interposed between thelight sources, and the padding is a two-sided adhesive tape.